Long channels for transistors

ABSTRACT

A semiconductor device includes a first nanosheet stack, a second nanosheet stack, and a third nanosheet stack arranged on a substrate. The semiconductor device includes a gate arranged on the first nanosheet stack, the second nanosheet stack, and the third nanosheet stack. The semiconductor device includes a channel extending through the gate and from the first nanosheet stack, the second nanosheet stack, and to the third nanosheet stack in a serpentine fashion. The semiconductor device includes a first source/drain and a second source/drain arranged on opposing sides of the gate.

BACKGROUND

The present invention generally relates to fabrication methods andresulting structures for semiconductor devices. More specifically, thepresent invention relates to long channels for transistors.

Semiconductor devices are formed using active regions of a wafer. Theactive regions are defined by isolation regions used to separate andelectrically isolate adjacent semiconductor devices. For example, in anintegrated circuit having a plurality of metal oxide semiconductor fieldeffect transistors (MOSFETs), each MOSFET has a source and a drain thatare formed in an active region of a semiconductor layer by implantingn-type or p-type impurities in the layer of semiconductor material.Disposed between the source and the drain is a channel (or body) region.Disposed above the body region is a gate electrode. The gate electrodeand the body are spaced apart by a gate dielectric layer.

SUMMARY

Embodiments of the present invention are directed to a method forfabricating a semiconductor device. A non-limiting example of the methodincludes forming a gate on a first nanosheet stack, a second nanosheetstack, and a third nanosheet stack arranged on a substrate. The methodincludes depositing a semiconductor material on the first nanosheetstack, the second nanosheet stack, and the third nanosheet stack. Themethod includes depositing an interlayer dielectric (ILD) on the firstnanosheet stack, the second nanosheet stack, and the third nanosheetstack. The method further includes forming a first trench and a secondtrench through the ILD on a first side of the gate, and a third trenchand a fourth trench through the ILD on a second side of the gate. Thesecond trench couples the second nanosheet stack to the third nanosheetstack, and the third trench couples the first nanosheet stack to thesecond nanosheet stack. The method includes depositing a metal in thefirst trench, the second trench, the third trench, and the fourthtrench.

A non-limiting example of the method for fabricating a semiconductordevice includes forming a gate on a first nanosheet stack, a secondnanosheet stack, and a third nanosheet stack arranged on a substrate.The first nanosheet stack, the second nanosheet stack, and the thirdnanosheet stack include alternating layers of silicon and silicongermanium. The method includes depositing a semiconductor material onthe layer of silicon of the first nanosheet stack, the second nanosheetstack, and the third nanosheet stack. The method includes depositing aninterlayer dielectric (ILD) on the first nanosheet stack, the secondnanosheet stack, and the third nanosheet stack. The method includesforming a first trench and a second trench through the ILD on a firstside of the gate, and a third trench and a fourth trench through the ILDon a second side of the gate. The second trench couples the secondnanosheet stack to the third nanosheet stack, and the third trenchcouples the first nanosheet stack to the second nanosheet stack. Themethod further includes depositing a metal in the first trench, thesecond trench, the third trench, and the fourth trench.

Embodiments of the invention are directed to a semiconductor device. Anon-limiting example of the semiconductor device includes a firstnanosheet stack, a second nanosheet stack, and a third nanosheet stackarranged on a substrate. The semiconductor device includes a gatearranged on the first nanosheet stack, the second nanosheet stack, andthe third nanosheet stack. The semiconductor device includes a channelextending through the gate and from the first nanosheet stack, thesecond nanosheet stack, and to the third nanosheet stack in a serpentinefashion. The semiconductor device includes a first source/drain and asecond source/drain arranged on opposing sides of the gate.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIGS. 1A-5B depict a method for forming a semiconductor device accordingto embodiments of the invention, in which:

FIG. 1A depicts a top view of a semiconductor device after forming adummy gate on nanosheet stacks;

FIG. 1B depicts a side view of the semiconductor device shown in FIG.1A;

FIG. 2A depicts a top view of a semiconductor device after performing anepitaxial growth process;

FIG. 2B depicts a side view of the semiconductor device shown in FIG.2A;

FIG. 3A depicts a top view of a semiconductor device after depositing aninterlayer dielectric (ILD) and replacing the dummy gate with a metalgate;

FIG. 3B depicts a side view of the semiconductor device shown in FIG.3A;

FIG. 4A depicts a top view of a semiconductor device after formingtrenches in the ILD;

FIG. 4B depicts a side view of the semiconductor device shown in FIG.4A;

FIG. 5A depicts a top view of a semiconductor device after depositing ametal in the trenches; and

FIG. 5B depicts a side view of the semiconductor device shown in FIG.5A;

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

In the accompanying figures and following detailed description of thedescribed embodiments, the various elements illustrated in the figuresare provided with two or three digit reference numbers. With minorexceptions, the leftmost digit(s) of each reference number correspond tothe figure in which its element is first illustrated.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related tosemiconductor device and integrated circuit (IC) fabrication may or maynot be described in detail herein. Moreover, the various tasks andprocess steps described herein can be incorporated into a morecomprehensive procedure or process having additional steps orfunctionality not described in detail herein. In particular, varioussteps in the manufacture of semiconductor devices andsemiconductor-based ICs are well known and so, in the interest ofbrevity, many conventional steps will only be mentioned briefly hereinor will be omitted entirely without providing the well-known processdetails.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, one particularly advantageous typeof MOSFET is known generally as a gate-all-around (GAA) nanosheet FET,which provides a relatively small FET footprint by forming the channelregion as a series of nanosheets. In a GAA configuration, ananosheet-based FET includes a source region, a drain region and stackednanosheet channels between the source and drain regions. A gatesurrounds the stacked nanosheet channels and regulates electron flowthrough the nanosheet channels between the source and drain regions. GAAnanosheet FETs are fabricated by forming alternating layers of channelnanosheets and sacrificial nanosheets. The sacrificial nanosheets arereleased from the channel nanosheets before the FET device is finalized.For n-type FETs, the channel nanosheets are silicon (Si), and thesacrificial nanosheets are silicon germanium (SiGe). For p-type FETs,the channel nanosheets are SiGe, and the sacrificial nanosheets are Si.

Integrated circuits, particularly input/output (I/O) circuits, needrelatively long channels (e.g., greater than 100 nanometers (nm)).Analog circuits used in system on chips (SOCs) or internet of things(IoTs) also use the long channel devices for special design purposes.However, fabrication methods for forming long channel devices adjacentto short channel devices need an extra mask over the long channel deviceduring replacement of the sacrificial dummy gate with the metal gate.The extra mask is needed to balance the gate metal recess budgetdifference between the long and short channel devices. The cost per areato fabricate conventional long channel devices is therefore large andinefficient.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention address the above-described shortcomings ofthe prior art by providing fabrication methods for forming a longchannel (greater than 100 nm in length) in a nanosheet device. The longchannel is formed by arranging a series of short channels in aserpentine (or zig-zag) arrangement. The channel length is determined bythe number of connected short channels, which provides the ability toeasily vary the length of the channel.

The above-described aspects of the invention address the shortcomings ofthe prior art by providing methods to form long channel devices with ashort channel compatible process. The methods eliminate the need for anextra mask during replacement of the sacrificial dummy gate with themetal gate. With these methods, the long channel devices have similarprocessing times as the short channel devices.

Turning now to a more detailed description of aspects of the presentinvention, FIGS. 1A-5B depict a method for forming a semiconductordevice 100 according to embodiments of the invention. FIG. 1A depicts atop view of a semiconductor device 100 after forming a dummy gate 110 onnanosheet stacks. FIG. 1B depicts a cross-sectional side view throughthe A-A′ axis of the semiconductor device 100 shown in FIG. 1A.

The semiconductor device 100 is a nanosheet FET and includes isolationregions 102 arranged on a semiconductor substrate 101. The isolationregions 102 are for isolation of active areas from one another.

Non-limiting examples of suitable substrate 101 materials include Si(silicon), strained Si, SiC (silicon carbide), Ge (germanium), SiGe(silicon germanium), SiGeC (silicon-germanium-carbon), Si alloys, Gealloys, III-V materials (e.g., GaAs (gallium arsenide), InAs (indiumarsenide), InP (indium phosphide), or aluminum arsenide (AlAs)), II-VImaterials (e.g., CdSe (cadmium selenide), CdS (cadmium sulfide), CdTe(cadmium telluride), ZnO (zinc oxide), ZnSe (zinc selenide), ZnS (zincsulfide), or ZnTe (zinc telluride)), or any combination thereof.

The isolation regions 102 can be formed by any known method in the art,including, for example, lithography or etching to form trenches, andthen filling the trenches with an insulating material, such as silicondioxide. In the exemplary embodiment, the isolation regions 102 areshallow trench isolation regions (STIs). However, the isolation region102 can be a trench isolation region, a field oxide isolation region(not shown), or any other equivalent known in the art. The isolationregions 102 provide isolation between neighboring gate structure regionsand can be used when the neighboring gates have opposite conductivities,i.e., nFETs and pFETs. As such, the at least one isolation region 102can separate an nFET device region from a pFET device region.

Nanosheet stacks 103 a (first nanosheet stack), 103 b (second nanosheetstack), and 103 c (third nanosheet stack) are arranged on the isolationregions 102 and the substrate 101. Although three nanosheet stacks 103a, 103 b, and 103 c are shown as an exemplary embodiment, thesemiconductor device 100 can include more than three nanosheet stacks inother embodiments. The nanosheet stacks 103 a, 103 b, 103 c can beformed in the substrate 101 by patterning a mask and then etching thesubstrate 101. The nanosheet stacks 103 a, 103 b, 103 c also can bepatterned in the substrate by, for example, sidewall imaging transfer.

The nanosheet stacks 103 a, 103 b, 103 c each include alternating layersof a first nanosheet 104 and a second nanosheet 105. The first nanosheet104 contacts the isolation region 102. The first nanosheet 104 is asemiconductor material, for example, silicon germanium in someembodiments. Other non-limiting examples of semiconductor materials forthe first nanosheet 104 include Si (silicon), strained Si, SiC (siliconcarbide), Ge (germanium), SiGeC (silicon-germanium-carbon), Si alloys,Ge alloys, GaAs (gallium arsenide), InAs (indium arsenide), InP (indiumphosphide), or any combination thereof.

The second nanosheet 105 alternates with the first nanosheet 104 in thenanosheet stacks 103 a, 103 b, and 103 c. The second nanosheet 105 is asemiconductor material, for example, silicon. Other non-limitingexamples of semiconductor materials for the second nanosheet 105 includestrained Si, SiC (silicon carbide), Ge (germanium), SiGe (silicongermanium), SiGeC (silicon-germanium-carbon), Si alloys, Ge alloys, GaAs(gallium arsenide), InAs (indium arsenide), InP (indium phosphide), orany combination thereof.

Although nanosheet stacks 103 a, 103 b, 103 c include four layers offirst nanosheet 104 and three layers of second nanosheet 105, thenanosheet stacks 103 a, 103 b, 103 c can include any number of firstnanosheets 104 and second nanosheets 105. The nanosheet stacks 103 a,103 b, 103 c can include one or more layers of each of first nanosheet104 and second nanosheet 105. For example, nanosheet stacks 103 a, 103b, 103 c can include one layer of first nanosheet 104 positioned incontact with the substrate 201 and one layer of second nanosheet 105disposed on the first nanosheet 105.

First and second nanosheets 301, 232 can be formed on the substrate 201by for example, forming alternating layers of first and secondnanosheets 104, 105 on the substrate 101, patterning the multi-layerstack into fin shaped structures, with the width of the fin structuresdefining the width of the nanosheets.

The height of the nanosheet stacks 103 a, 103 b, and 103 c generallyvary, as it depends on the type of device, and is not intended to belimited. In the exemplary embodiment, the pitch 120 of the nanosheetstacks (between nanosheet stack 103 a and 103 b, and between 103 b and103 c) is at least 30 nm.

The semiconductor device 100 includes a gate 110 arranged on the firstnanosheet stack 103 a, second nanosheet stack 103 b, and third nanosheetstack 103 c. The gate 110 is a “dummy gate” and includes a sacrificialgate material (dummy gate material). The sacrificial gate material canbe, for example, amorphous silicon or polysilicon.

The gate 110 includes gate spacers 111. The gate spacers 111 include adielectric material, for example, silicon dioxide, silicon nitride,SiOCN, or SiBCN. Other non-limiting examples of materials for the gatesspacers 111 include dielectric oxides, dielectric nitrides, dielectricoxynitrides, or any combination thereof.

FIG. 2A depicts a top view of the semiconductor device 100 afterperforming an epitaxial growth process. FIG. 2B depicts across-sectional side view through the A-A′ axis of the semiconductordevice 100 shown in FIG. 2A.

The epitaxial growth process deposits epitaxial growth 210 on thesemiconductor material of the nanosheet stacks 103 a, 103 b, and 103 c.The epitaxial growth 210 does not overlap on neighboring nanosheetstacks when the pitch 120 (see FIG. 1B) of the nanosheet stacks is largeenough. The terms “epitaxial growth and/or deposition” and “epitaxiallyformed and/or grown” mean the growth of a semiconductor material(crystalline material) on a deposition surface of another semiconductormaterial (crystalline material), in which the semiconductor materialbeing grown (crystalline overlayer) has substantially the samecrystalline characteristics as the semiconductor material of thedeposition surface (seed material). Epitaxial semiconductor materialscan be grown from gaseous or liquid precursors. Epitaxial materials canbe grown using vapor-phase epitaxy (VPE), molecular-beam epitaxy (MBE),liquid-phase epitaxy (LPE), or other suitable process. Epitaxialsilicon, silicon germanium, and/or carbon doped silicon (Si:C) can bedoped during deposition (in-situ doped) by adding dopants, n-typedopants (e.g., phosphorus or arsenic) or p-type dopants (e.g., boron orgallium), depending on the type of transistor.

The first nanosheets 104 in the source/drain regions outside the gatecan be selectively removed according to some embodiments afterperforming the epitaxial growth process. In other embodiments, the firstnanosheets 104 are not removed.

FIG. 3A depicts a top view of a semiconductor device 100 afterdepositing an interlayer dielectric (ILD) 332 on the nanosheet stacksand replacing the dummy gate 110 with a metal gate 330. FIG. 3B depictsa cross-sectional side view through the A-A′ axis of the semiconductordevice 100 shown in FIG. 3A.

The ILD 332 is deposited on and around the nanosheet stacks 103 a, 103b, and 103 c and around the metal gate 330. The ILD 332 can be formedfrom, for example, a low-k dielectric material (with k<4.0), includingbut not limited to, silicon oxide, spin-on-glass, a flowable oxide, ahigh density plasma oxide, borophosphosilicate glass (BPSG), or anycombination thereof. The ILD 332 can be deposited by a depositionprocess, including, but not limited to CVD, PVD, plasma enhanced CVD,atomic layer deposition (ALD), evaporation, chemical solutiondeposition, or like processes.

The metal gate 330 includes metal gates formed, for example, by fillinga dummy gate opening (after removing the sacrificial gate material) withone or more dielectric materials, one or more workfunction metals, andone or more metal gate conductor materials. The gate dielectricmaterial(s) can be a dielectric material having a dielectric constantgreater than about 3.9, about 7.0, or about 10.0. Non-limiting examplesof suitable materials for the dielectric material include oxides,nitrides, oxynitrides, silicates (e.g., metal silicates), aluminates,titanates, nitrides, or any combination thereof. Examples of high-kmaterials (with a dielectric constant greater than 7.0) include, but arenot limited to, metal oxides such as hafnium oxide, hafnium siliconoxide, hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminumoxide, zirconium oxide, zirconium silicon oxide, zirconium siliconoxynitride, tantalum oxide, titanium oxide, barium strontium titaniumoxide, barium titanium oxide, strontium titanium oxide, yttrium oxide,aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. Thehigh-k material can further include dopants such as, for example,lanthanum and aluminum.

The work function metal(s) can be disposed over the gate dielectricmaterial. The type of work function metal(s) depends on the type oftransistor and can differ between an nFET and a pFET. Non-limitingexamples of suitable work function metals include p-type work functionmetal materials and n-type work function metal materials. P-type workfunction materials include compositions such as ruthenium, palladium,platinum, cobalt, nickel, and conductive metal oxides, or anycombination thereof. N-type metal materials include compositions such ashafnium, zirconium, titanium, tantalum, aluminum, metal carbides (e.g.,hafnium carbide, zirconium carbide, titanium carbide, and aluminumcarbide), aluminides, or any combination thereof. The work functionmetal(s) can be deposited by a suitable deposition process, for example,CVD, PECVD, PVD, plating, thermal or e-beam evaporation, and sputtering.

A conductive metal is deposited over the dielectric material(s) andworkfunction layer(s) to form the metal gates 330. Non-limiting examplesof suitable conductive metals include aluminum (Al), platinum (Pt), gold(Au), tungsten (W), titanium (Ti), or any combination thereof. Theconductive metal can be deposited by a suitable deposition process, forexample, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, andsputtering. A planarization process, for example, chemical mechanicalplanarization (CMP), is performed to polish the surface of theconductive gate metal.

FIG. 4A depicts a top view of the semiconductor device 100 after formingtrenches in the ILD 332. FIG. 4B depicts a cross-sectional side viewthrough the A-A′ axis of the semiconductor device 100 shown in FIG. 4A.

On one side (first side 440) of the metal gate 330, a first trench 401is formed over the first nanosheet stack 103 a, and a second trench 402is formed over the second nanosheet stack 103 b and third nanosheetstack 103 c. The first trench 401 extends through the ILD 332 to theepitaxial growth 210 on the first nanosheet stack 103 a. The secondtrench 402 extends through the ILD 332 to the epitaxial growth 210 onthe second nanosheet stack 103 b and third nanosheet stack 103 c. Thesecond trench 402 is wider than the first trench 401 so that oncefilled, the second nanosheet stack 103 b and third nanosheet stack 103 cwill be electrically connected (coupled) on the first side 440 of themetal gate 330. The first and second nanosheet stacks 103 a and 103 bare isolated from one another on the first side 440 of the gate 330.

On the other side (second side 441) of the metal gate 330 (see FIG. 4A),a third trench 403 is formed over the first nanosheet stack 103 a andsecond nanosheet stack 103 b, and a fourth trench 404 is formed over thethird nanosheet stack 103 c. The third trench 403 extends through theILD 332 to the epitaxial growth 210 on the first nanosheet stack 103 aand second nanosheet stack 103 b. The fourth trench 404 extends throughthe ILD 332 to the epitaxial growth 210 on the third nanosheet stack 103c. The third trench 403 is wider than the fourth trench 404 so that oncefilled, the first nanosheet stack 103 a and the second nanosheet stack103 c will be electrically connected (coupled) on the other side (secondside 441) of the metal gate 330. The second and third nanosheet stacks103 b and 103 c are isolated from one another on the second side 441 ofthe gate 330.

The trenches (first trench 401, second trench 402, third trench 403, andfourth trench 404) can be formed by removing portions of the ILD 332 bya suitable etch process. According to one or more embodiments, the etchprocess used to form the trenches is a reactive ion etch (RIE).

FIG. 5A depicts a top view of the semiconductor device 100 afterdepositing metal 550 in the trenches. FIG. 5B depicts a cross-sectionalside view through the A-A′ axis of the semiconductor device 100 shown inFIG. 5A.

The metal 550 fills the first trench 401, second trench 402, thirdtrench 403, and fourth trench 404. Using alternating trenches ofdifferent widths to connect (couple) a set of nanosheet stacks on thefirst side 440 of the gate 330 (second nanosheet stack 103 b and thirdnanosheet stack 103 c) and then to connect (couple) that pair ofnanosheet stacks with another nanosheet stack (second nanosheet stack103 b and third nanosheet stack 103 c) on the other side (second side441) of the gate 330 enables formation of a long serpentine channel 590that crosses through the metal gate 330 in three areas. The channel 590connects (couples) the first nanosheet stack 103 a, the second nanosheetstack 103 b, and the third nanosheet stack 103 c. The first nanosheetstack 103 a and the second nanosheet stack 103 b are connected (coupled)on one side of the gate by a metal-filled trench, and the secondnanosheet stack 103 b and the third nanosheet stack 103 c are connected(coupled) on another side of the gate by a metal-filled trench.

Source/drains 501, 502 are arranged on opposing sides of the gate 330 atthe terminal ends of the serpentine channel 590 (see FIGS. 5A and 5C).

The metal 550 can include one or more layers of conductive metalmaterials that depends on the type of transistor and can provide lowcontact resistance. According to some embodiments, the metal 550includes a liner layer and a metal fill. Non-limiting examples ofmaterials for the liner layer include Co, Ti, CoTi, Ni, Pt, NiPt,NiPtTi, Ta, TaNi, TaAl, TaAlN, TiN, TiAl, TiAlN, or any combinationthereof. The one or more layers/films making up the liner layer can beformed by a chemical vapor deposition process (CVD), atomic layerdeposition (ALD), or other suitable process. The metal fill deposited onthe liner layer is a conductive metal, for example, aluminum (Al),platinum (Pt), gold (Au), tungsten (W), titanium (Ti), or anycombination thereof. The conductive metal can be deposited by a suitabledeposition process, for example, CVD, PECVD, PVD, plating, thermal ore-beam evaporation, or sputtering. After deposition, a planarizationprocess, for example, chemical mechanical planarization (CMP) isperformed to remove any conductive material from the surface of the ILD332.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

The phrase “selective to,” such as, for example, “a first elementselective to a second element,” means that the first element can beetched and the second element can act as an etch stop.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

As previously noted herein, for the sake of brevity, conventionaltechniques related to semiconductor device and integrated circuit (IC)fabrication may or may not be described in detail herein. By way ofbackground, however, a more general description of the semiconductordevice fabrication processes that can be utilized in implementing one ormore embodiments of the present invention will now be provided. Althoughspecific fabrication operations used in implementing one or moreembodiments of the present invention can be individually known, thedescribed combination of operations and/or resulting structures of thepresent invention are unique. Thus, the unique combination of theoperations described in connection with the fabrication of asemiconductor device according to the present invention utilize avariety of individually known physical and chemical processes performedon a semiconductor (e.g., silicon) substrate, some of which aredescribed in the immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an IC fall into four general categories, namely, filmdeposition, removal/etching, semiconductor doping andpatterning/lithography. Deposition is any process that grows, coats, orotherwise transfers a material onto the wafer. Available technologiesinclude physical vapor deposition (PVD), chemical vapor deposition(CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE)and more recently, atomic layer deposition (ALD) among others.Removal/etching is any process that removes material from the wafer.Examples include etch processes (either wet or dry), andchemical-mechanical planarization (CMP), and the like. Semiconductordoping is the modification of electrical properties by doping, forexample, transistor sources and drains, generally by diffusion and/or byion implantation. These doping processes are followed by furnaceannealing or by rapid thermal annealing (RTA). Annealing serves toactivate the implanted dopants. Films of both conductors (e.g.,poly-silicon, aluminum, copper, etc.) and insulators (e.g., variousforms of silicon dioxide, silicon nitride, etc.) are used to connect andisolate transistors and their components. Selective doping of variousregions of the semiconductor substrate allows the conductivity of thesubstrate to be changed with the application of voltage. By creatingstructures of these various components, millions of transistors can bebuilt and wired together to form the complex circuitry of a modernmicroelectronic device. Semiconductor lithography is the formation ofthree-dimensional relief images or patterns on the semiconductorsubstrate for subsequent transfer of the pattern to the substrate. Insemiconductor lithography, the patterns are formed by a light sensitivepolymer called a photo-resist. To build the complex structures that makeup a transistor and the many wires that connect the millions oftransistors of a circuit, lithography and etch pattern transfer stepsare repeated multiple times. Each pattern being printed on the wafer isaligned to the previously formed patterns and slowly the conductors,insulators and selectively doped regions are built up to form the finaldevice.

The flowchart and block diagrams in the Figures illustrate possibleimplementations of fabrication and/or operation methods according tovarious embodiments of the present invention. Variousfunctions/operations of the method are represented in the flow diagramby blocks. In some alternative implementations, the functions noted inthe blocks can occur out of the order noted in the Figures. For example,two blocks shown in succession can, in fact, be executed substantiallyconcurrently, or the blocks can sometimes be executed in the reverseorder, depending upon the functionality involved.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments described. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein.

What is claimed is:
 1. A method for fabricating a semiconductor device,the method comprising: forming a gate on a first nanosheet stack, asecond nanosheet stack, and a third nanosheet stack arranged on asubstrate; depositing a semiconductor material on the first nanosheetstack, the second nanosheet stack, and the third nanosheet stack;depositing an interlayer dielectric (ILD) on the first nanosheet stack,the second nanosheet stack, and the third nanosheet stack; forming afirst trench and a second trench through the ILD on a first side of thegate, and a third trench and a fourth trench through the ILD on a secondside of the gate, the second trench coupling the second nanosheet stackto the third nanosheet stack, and the third trench coupling the firstnanosheet stack to the second nanosheet stack; and depositing a metal inthe first trench, the second trench, the third trench, and the fourthtrench.
 2. The method of claim 1, wherein a pitch between the firstnanosheet stack and the second nanosheet stack comprises at least 30nanometers (nm).
 3. The method of claim 1, wherein depositing thesemiconductor material comprises applying an epitaxial growth process.4. The method of claim 1, wherein subsequent to depositing the metal achannel is formed that crosses through the gate in three areas.
 5. Themethod of claim 1, wherein the first trench extends through the ILD tothe semiconductor material on the first nanosheet stack.
 6. The methodof claim 5, wherein the second trench extends through the ILD to thesemiconductor material on the second nanosheet stack and the thirdnanosheet stack.
 7. The method of claim 1, wherein the third trenchextends through the ILD to the semiconductor material on the firstnanosheet stack and the second nanosheet stack, and the fourth trenchextends through the ILD to the semiconductor material on the thirdnanosheet stack.
 8. A method for fabricating a semiconductor device, themethod comprising: forming a gate on a first nanosheet stack, a secondnanosheet stack, and a third nanosheet stack arranged on a substrate,the first nanosheet stack, the second nanosheet stack, and the thirdnanosheet stack comprising alternating layers of silicon and silicongermanium; depositing a semiconductor material on the layer of siliconof the first nanosheet stack, the second nanosheet stack, and the thirdnanosheet stack; depositing an interlayer dielectric (ILD) on the firstnanosheet stack, the second nanosheet stack, and the third nanosheetstack; forming a first trench and a second trench through the ILD on afirst side of the gate, and a third trench and a fourth trench throughthe ILD on a second side of the gate, the second trench coupling thesecond nanosheet stack to the third nanosheet stack, and the thirdtrench coupling the first nanosheet stack to the second nanosheet stack;and depositing a metal in the first trench, the second trench, the thirdtrench, and the fourth trench.
 9. The method of claim 8, wherein a pitchof the first nanosheet stack and the second nanosheet comprises at least30 nanometers (nm).
 10. The method of claim 8, wherein depositing thesemiconductor material is by an epitaxial growth process.
 11. The methodof claim 10, wherein the semiconductor material deposited on the firstnanosheet stack and the second nanosheet stack does not overlap eachanother.
 12. The method of claim 8, wherein after depositing the metal,a channel is formed that crosses through the gate in three areas. 13.The method of claim 8, wherein the gate comprises a sacrificial gatematerial.
 14. The method of claim 13, wherein the gate is replaced witha metal gate stack before forming the first trench on the first side ofthe gate and the second trench on the second side of the gate.